Typically, gas turbine engines include a compressor for compressing air, a combustor for mixing the compressed air with fuel and igniting the mixture, and a turbine blade assembly for producing power. Combustors often operate at high temperatures that may exceed 2,500 degrees Fahrenheit. Typical turbine combustor configurations expose turbine blade and vane assemblies to these high temperatures. As a result, turbine rotating blades and turbine stationary vanes (hereafter “turbine airfoils”) must be made of materials capable of withstanding such high temperatures. In addition, turbine airfoils often contain cooling systems for prolonging the life of the turbine airfoils and reducing the likelihood of failure as a result of excessive temperatures.
Typically, turbine blades are formed from a root portion and a platform, or end wall, at one end and a generally elongated airfoil forming a blade that extends radially outward from the end wall. The blade is ordinarily composed of a tip opposite the root section, a leading edge, a trailing edge, a pressure side wall and a suction side wall. A turbine blade typically includes a fillet on the outer surface of the blade along the intersection of the generally elongated airfoil and the end walls. The inner aspects of most turbine blades contain an intricate maze of cooling channels forming a cooling system. The cooling channels in the blades may receive air from the compressor of the turbine engine and pass the air through the airfoil.
Turbine vanes are formed from a generally elongated airfoil, having a first end wall on one end and a second end wall on the opposite end of the airfoil. The airfoil itself generally has a leading edge, a trailing edge, a pressure side wall and a suction side wall. The elongated portion of the vane extends radially between the first end wall and the second end wall. A turbine vane may include a first fillet along the intersection of the generally elongated airfoil and the first end wall, and a second fillet along the intersection of the generally elongated airfoil and the second end wall. Much like blades, the inner aspects of most turbine vanes contain cooling channels forming a cooling system.
The cooling channels often include multiple flow paths that are designed to maintain the turbine airfoil at a relatively uniform temperature. However, localized hot spots may form where parts of the turbine airfoil are not adequately cooled. These localized hot spots may damage the turbine airfoil and may eventually necessitate replacement of the turbine airfoil.
One area of a turbine airfoil that is particularly difficult to cool is the fillet at the intersection between the generally elongated airfoil and the end wall. Such difficulty cooling fillets is a result of several factors. First, in order to handle high localized stress, the fillet is generally thicker than adjacent turbine airfoil components. Thus, conventional impingement cooling and convection cooling of the inner surface of the generally elongated airfoil or end plate is less effective for cooling the fillet region. Second, due to the high local Stresses, convection cooling holes that penetrate the outer surface of the fillet are not desirable because such holes may concentrate the local stresses thereby significantly reducing the useful life of the turbine airfoil. Finally, film cooling along the outer surface of the fillet generally provides only limited cooling to the fillet because the horseshoe vortex may sweep the film away from the fillet or the film has mixed with hot gases prior to reaching the fillet thereby substantially reducing the film's effectiveness. Thus, a need exists for providing effective direct cooling of blade fillets and vane fillets without reducing the useful life of the blades or vanes.